Types of Dynamic Microphones

Judging by their numbers, dynamic microphones are the most popular type of microphone, and for a very good reason, they are cheap and very robust. The most recognisable are Shure dynamic microphones, Shure SM58 microphones are used principally as vocal microphones on stage and occasionally in the studio condenser microphones are usually used for vocal duties in the recording studio). Its sibling the Shure SM57 are used as drum microphones (particularly snare drums) and instrument microphones (usually guitar amplifiers) both in the studio and for Live work.

The dynamic microphone works like a speaker in reverse, think of the speaker cone as the diaphragm and the attached coil is in the magnetic housing. Instead of an alternating current being supplied to cause a magnetic field that attracts and repels the cone, the diaphragm acts as a generator of alternating current but at a much lower power than that necessary to power a speaker. (Some people have experimented using speakers as microphones but because the speaker cone is not very sensitive to the movement of air, it won't work very well.)

So as you can see the dynamic microphone requires no external power supply (the energy comes from the movement of air) and is virtually immune to distortion.

The Downsides of Dynamic Microphones

Dynamic microphones have two downsides, their poor high frequency response and a low output level. The former is caused by the relatively large mass of the diaphragm with its attached coil plus the effects of magnetic damping, and the latter is due to the small current that is produced.

These downsides of a dynamic microphone dictate its usage, it is used in situations where its typical upper limit of 15khz frequency response doesn't matter e.g. the human voice doesn't go up to 20khz (which is considered the upper limit of human hearing) and in close proximity to the sound source.

You wouldn't use a dynamic microphone for recording an orchestra since the frequencies exceed the microphone's capabilities and the low output would mean that in the quiet moments e.g. a harp solo you would need to add so much gain in the mixer that you would hear lots of hiss. High quality recording microphones needed in this situation would be condenser microphones.

Although not exactly a downside, another consideration is the physical size of the dynamic microphone capsule, this prevents it from being used where a very small size is important. Dynamic microphones are used a lot in radio microphones because they don’t require any power, so the batteries are used just for the transmitter, these can be headset microphones or handheld microphones.

Other Popular Uses of Dynamic mics

They can be used as video microphones when plugged into the extermnal microphone input of the camera, where they can be used for a presenter and interviewee for instance, either in the form of clip microphones (sometimes called lapel microphones or lavalier microphones).

Because they are often used in a Live situation dynamic microphones are usually used in close proximity to the sound source and usually have a cardioid response to avoid ‘feedback’ or ‘howl round’, so the microphone’s bass response is rolled off progressively to compensate for the proximity effect (bass frequencies are accentuated the closer the microphone is to the source) and there is often a boost or presence peak at about 3khz to help singing and speech to be clearer through the P.A. system. This is why it isn’t advisable to use dynamic microphones as boom microphones or for recording general sounds since the sound would be bass-light and overly bright in the mid frequencies.

Dynamic microphones tend not to be used as computer microphones or usb microphones because they are prone to picking up interference from the powerful electro-magnetic fields in the monitor. Electret microphones are usually used in this case because they are cheap to produce and their power supply comes from the computer.

Dynamic Microphones - Summary

Cheap, robust and don’t require external power. Used as vocal microphones mostly in a Live situation, also as drum and instrument microphones (Studio and Live) where the highest frequency to be recorded isn’t typicallly above 15khz and desktop microphones at conferences. Wireless microphones (both handheld microphones and headset microphones) and external video microphones for speech recording, mostly as clip microphones. Not suitable as high quality recording microphones due to poor high frequency response and low output.

Dynamic microphones are not suitable as computer microphones or usb microphones due to susceptibility of electrical interference from the monitor.

Shure Dynamic microphones are the most common e.g. Shure SM58 microphones and they will serve you well, but try out other manufacturers microphones as well since each one has different attributes such as frequency response, polar response (cardioid, hypercardioid etc), immunity from handling and wind noise and more personal aspects such as colour and style.